Production of an x-ray beam by electron bombardment of a target dates back to the early 1900's. The early x-ray tube consisted of a gas-filled glass envelope containing a cathode and an anode (target). By imposing a high voltage charge between cathode and anode, a glow discharge took place, causing electron bombardment of the target and production of x-ray energy. Later improvements consisted of evacuating the atmosphere around the cathode and anode elements, and the use of a hot tungsten filament within the cathode, permitting the focusing of the electron beam. It was then possible to generate an x-ray beam from a more closely controlled bombardment source, thereby yielding greater diagnostic detail. Finally, a rotating target structure was developed in the early 1940's which permitted a further shrinking of the electron bombardment area, opening up even greater possibilities for improved diagnostic techniques.
Current diagnostic x-ray tubes contain rotating anodes on which targets, which weigh as much as one kilogram, rotate at speeds up to 10,000 rpm. Because of a number of factors, such as thermal expansion and contraction, and high acceleration and deceleration torques, these structures may have a short life due to bearing and unbalance problems. Accordingly, a need has arisen for an x-ray tube structure which has increased structural strength and stability under the extreme operating conditions typical in an x-ray tube.